In nature, flu viruses circulate continuously among animals, especially birds. In Phase 1 no viruses circulating among animals have been reported to cause infections in humans.

In Phase 2 an animal flu virus circulating among domesticated or wild animals is known to have caused infection in humans, and is considered a potential pandemic threat.

In Phase 3, an animal or human-animal flu reassortant virus has caused sporadic cases or small clusters of disease in people, but has not resulted in human-to-human transmission sufficient to sustain community-level outbreaks and/or to cause a pandemic.

Phase 4 is characterized by verified human-to-human transmission of an animal or human-animal influenza reassortant virus able to cause “community-level outbreaks.” The ability to cause sustained disease outbreaks in a community marks a significant upwards shift in the risk for a pandemic. Phase 4 indicates a significant increase in risk of a pandemic but does not necessarily mean that a pandemic is a forgone conclusion.

Phase 5 is characterized by human-to-human spread of the virus into at least two countries in one WHO region. While most countries will not be affected at this stage, the declaration of Phase 5 is a strong signal that a pandemic is imminent and that the time to finalize the organization, communication, and implementation of the planned mitigation measures is short.

Phase 6, the pandemic phase, is characterized by community level outbreaks in at least one other country in a different WHO region in addition to the criteria defined in Phase 5. Designation of this phase will indicate that a global pandemic is under way.

Technology, partnered with the work done by health experts on SARS and avian flu over the past few years, allows WHO to track the birth of a pandemic in real time.

They’re watching to see how it’s transmitted, the spectrum of disease in various populations (different age groups, cultures, and levels of medical care, etc), and how the virus itself may be changing, or mutating.

“This change to a higher phase of alert is a signal to governments, to ministries of health and other ministries, to the pharmaceutical industry and the business community that certain actions should now be undertaken with increased urgency, and at an accelerated pace.”

Disclaimer

The information on PKIDs' Blog is for educational purposes only and should not be considered to be medical advice. It is not meant to replace the advice of the physician who cares for you or your child. All medical advice and information should be considered to be incomplete without a physical exam, which is not possible without a visit to your doctor.